You can slit down one side of the pepper, use a spoon or something, and scrap out the seeds and white membrane. The heat is in the membrane that holds the seeds to the interior walls of the pepper.
If you want to can them whole, you can can them with blanched carrot chunks, other veggie chunks like cauliflower or whole sweet peppers, and the carrots, veggies, and sweet peppers will draw off some of the heat. This makes a nice giardiniara:
http://allrecipes.com/Recipe/hot-ita...ra/detail.aspx